1. Field of the Invention
The present invention relates to a zoom lens optical system suitable for a camera using a solid state imaging device, and more particularly, to a zoom lens optical system which can be made compact, correct color aberration, ensure a high zooming ratio, and have low manufacturing costs.
2. Description of the Related Art
Electronic still cameras and video cameras using a solid state imaging device, such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), are rapidly becoming more prevalent. Such cameras are being developed cheaper, lighter, and more compact. Accordingly, a zoom lens optical system used in these cameras is also required to be less expensive, lighter, and more compact.
Japanese Patent Publication No. 2004-109653 (Apr. 8, 2004) discloses a 4-group zoom lens optical system. The zoom lens optical system includes a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, arranged sequentially from an object. The zoom lens optical system performs zooming by moving the first through fourth lens groups. The first lens group and the third lens group when at a telephoto position of their ranges are closer to the object than when at a wide angle position of their ranges. Since the first lens group has a single lens, color aberration compensation by the first lens group is difficult. Since the zoom lens optical system is long, product value decreases.
Japanese Patent Publication No. 2001-356269 (Dec. 26, 2001) discloses a 4-group zoom lens optical system. The zoom lens optical system includes a first lens group having a single positive lens, a second lens group having at least one negative lens and one positive lens, a third lens group having one negative lens and two positive lenses, and a fourth lens group having at least one positive lens, arranged sequentially from an object. The zoom lens optical system performs zooming by moving the first through third lens groups. The zoom lens optical system has the drawback in that color aberration compensation is difficult since the first lens group has the single lens. Also, since the fourth lens group has two or more lenses, the number of lenses increase, thereby increasing production costs and requiring a large receiving space.
U.S. Patent Publication No. 2003/0002171 A1 (Jan. 2, 2003) discloses a 4-group zoom lens optical system. The zoom lens optical system includes first through fourth lens groups sequentially arranged from an object. The zoom lens optical system performs zooming by operating the first through fourth lens groups and causing a change in space between the first lens group and the second lens group. The zoom lens optical system has an advantage in that color aberration can be easily corrected since the first lens group has three lenses. However, the third lens group has four or more lenses, and thus production costs increase. Also, aspherical materials of the third lens group and the fourth lens group are incompatible, and thus the system is expensive and difficult to manufacture.
Japanese Patent Publication No. 2003-177317 (Jun. 27, 2003) discloses a 4-group zoom lens optical system which performs zooming by operating first, third, and fourth lens groups. The first lens group has three lenses, the second lens group has four lenses, the third lens group has two positive lenses and a negative lens, and the fourth lens group has three lenses. Since each of the first lens group and the fourth lens group has three lenses, aberration is reduced, but it is difficult to make the zoom lens optical system inexpensive and compact due to the increase in the number of lenses.
Japanese Patent Publication No. 2002-107629 (Apr. 10, 2002) discloses a 4-group zoom lens optical system which operates all of first through fourth lens groups. The first lens group has three lenses, the second lens group has four lenses, the third lens group has two positive lenses and a negative lens, and the fourth lens group has five lenses. In this case, color aberration and astigmatic field curvature can be corrected since the first lens group has three lenses. However, since the number of lenses increases, automatic focusing is difficult and the size and costs of the zoom lens optical system increase.